The Warragamba Dam hit full capacity and began spilling at 7pm Friday.

Some 900 people in western Sydney are on stand-by for evacuation should the SES give the order.

The Bureau of Meteorology says a Flood Watch for moderate flooding is current for the catchment based on forecast rain for the next two to three days.

NSW SES spokesman Phil Campbell says the water is rising.

"We are seeing rises already in the Hawkesbury Nepean River system and that's due to inflows from other rivers like the Colo, the Gross and the Nepean rivers and water coming out of the creeks in Sydney," he told 702 ABC Evenings at 6.30pm Friday.

"The concern for us is that with the additional water once Warragamba Dam begins to spill we will begin to see a faster rise in that water in Western Sydney.

"The expectation at this stage is for water levels of somewhere between 10 and 12 metres from what the Bureau of Meteorology has told us.

Also, updated information from the Bureau of Meteorology has seen revised bridge and ferry closure times for the Hawkesbury Nepean area.

Rainfall rates in the catchment have eased overnight and with the revised figures, the bridges at North Richmond and Windsor are expected to close from between Saturday afternoon and Sunday.

The river at the North Richmond bridge is expected to hit 6 metres around 9am Saturday with minor flooding.

Further rises to moderate flood level late Saturday 3rd March 2012 and Sunday 4th March 2012 with further forecast rain.

Other impacts include;

The Sackville Ferry ceased operation at 12.00am Saturday 3rd March 2012. The Yarramundi Bridge was closed at 3.30am Saturday 3rd March 2012. The Wallacia Bridge may be closed as a consequence of the flooding.

The Lower Portland Ferry are likely to close over the weekend. The Webbs Creek Ferry and the ferry at Wiseman's Ferry may also be affected.

The Colo River at Putty Road is expected to reach 5.7m on Saturday afternoon, and 7.0m early Sunday morning with further rises possible.

The SES says that most areas along the Hawkesbury-Nepean river system are under the minor flood level at the moment. Hundreds of people remain on stand-by to evacuate.

"Those evacuation warnings are still current for properties in Pitt Town, Richmond lowlands, Grono's point as well as the low lying areas along the river banks between Windsor and Wiseman's ferry," said NSW SES spokesperson Andrew Richards

A Flood Watch remains current for the catchment based on forecast rain for the next two to three days.

"Severe weather can be very dangerous and people need to be aware that under no circumstances should they enter floodwater," NSW SES Assistant Commissioner Keith Fitzgerald says.

The SES says it has doorknocked about 340 properties which are likely to be affected.

The affected areas include the Richmond Lowlands area, including Cornwallis, low lying areas at the northern part of Richmond, Richmond Lowlands, low lying areas at the western part of Hobartville, and lowlying areas in the northern part of Agnes Banks.

The SES' Assistant Commissioner Keith FitzGerald says the need for an evacuation was delayed because of the slight easing in rain overnight, but the flood evacuation warning remains in place.

"Residents should monitor the situation and be prepared to evacuate when instructed to do so," he said in a statement.

The NSW SES has also warned residents of the Wallacia and Nepean caravan parks to be prepared to evacuate.

If this is required, the SES will issue a Flood Evacuation Order.

Across the state, the biggest concern tonight was Bathurst in the Central West, he says.

"We are fairly concerned about the city of Bathurst...We do now have the town cut in two with the Great Western Highway closed.

"It will be a difficult night in Bathurst for those trying to get around but the amount of flooding of properties is quite minimal."

As the rain heads south, Mr Campbell says Cooma, Goulburn, Tumut and Queanbeyan will again be in the firing line.

Eleven people were rescued in Tumut during flooding, and there is the potential for further rain and flooding, he says.

The SES has maintained its evacuation orders for Goulburn and Cooma, with the potential for a further 100 to 200mm of rain in the area.

There is a further evacuation warning for 400 people in Queanbeyan and 900 people in western Sydney to prepare to leave their places should the situation worsen.

"For those people it's just a watch and wait... and if we have concerns for their safety we will issue an evacuation order and ask those people to leave."

The SES is also concerned about the Lachlan and Murrumbidgee Rivers.

The NSW Police says it has activated the Public Information and Inquiry Centre in support of the NSW SES following the flood activity.

The Public Information and Inquiry Centre can be contacted by telephone on 1800 227 228.

Members of the public seeking emergency assistance during a flood or storm should call the NSW State Emergency Service on 132 500.